Loratadine with Cimetidine Interaction Details
Brand Names Associated with Loratadine
- Agistam®
- Alavert®
- Alavert® D (as a combination product containing Loratadine, Pseudoephedrine)
- Claritin-D® (as a combination product containing Loratadine, Pseudoephedrine)
- Claritin®
- Clear-Atadine®
- Dimetapp® ND
- Loratadine
- Tavist® Non-Sedating
- Wal-itin®
Brand Names Associated with Cimetidine
- Cimetidine
- Tagamet®
- Tagamet® HB

Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Nov 05, 2023
Interaction Effect
Increased loratadine serum concentrations; possible loratadine toxicity
Interaction Summary
Coadministered oral doses of loratadine and cimetidine produce an increase in loratadine serum concentrations. No significant adverse effects, however, were reported as a result of this comedication, although the studies were done in healthy volunteers receiving a 10-day course of loratadine.
Severity
Minor
Onset
Rapid
Evidence
Probable
How To Manage Interaction
When loratadine is coadministered with cimetidine, monitor patients for signs of sedative or anticholinergic effects. If necessary, lower the doses of either or both medications.
Mechanism Of Interaction
Decreased loratadine metabolism
Literature Reports
A) When long-acting loratadine 10 mg per day was given concomitantly with cimetidine 300 mg four times a day, increases in the area under the concentration-time curve (AUC) for loratadine and its major active metabolite descarboethoxyloratadine were 103% and 6%, respectively . Twenty-four normal volunteers received a 10-day course of these medications. No clinically relevant changes were found. Clinical effects were assessed by laboratory and cardiographic testing, vital signs, and adverse events. No incidents of sedation or syncope were reported, and no significant alterations in QTc interval occurred. Cimetidine serum concentrations were unaffected.
B) Concomitant administration of loratadine and cimetidine significantly increased the loratadine plasma concentrations and desloratadine concentrations when compared with administration of loratadine alone. Cimetidine concentrations were unaffected by loratadine coadministration. A randomized, evaluator-blind, multiple dose, three-way crossover drug interaction study in which 24 volunteers received either loratadine 10 mg daily or placebo, with cimetidine 300 mg four times daily for 10 days, was conducted. Coadministration of loratadine and cimetidine when compared to loratadine alone increased mean loratadine Cmax from 4.73 to 8.14 ng/mL and AUC (0-24h) from 24.1 to 40.9 ng/mL hr however, desloratadine concentrations remained similar Cmax (5.55 vs 5.25 ng/mL hr) and AUC (0-24h) (88.2 vs 83 ng/mL hr). Compared with administraion of cimetidine alone, coadministration of loratadine and cimetidine gave similar mean cimetidine Cmax (1.64 vs. 1.76 mcg/mL) and AUC (0-24h) (18.1 vs 19.2 mcg/mL hr). No clinically significant changes in cardiac repolarization parameters were observed. The study demonstrated that although a significant pharmacokinetics drug interaction with cimetidine and loratadine exists, this effect was not accompanied by a change in the QT interval .
Loratadine Overview
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Loratadine is used to temporarily relieve the symptoms of hay fever (allergy to pollen, dust, or other substances in the air) and other allergies. These symptoms include sneezing, runny nose, and itchy eyes, nose, or throat. Loratadine is also used to treat itching and redness caused by hives. However, loratadine does not prevent hives or other allergic skin reactions. Loratadine is in a class of medications called antihistamines. It works by blocking the action of histamine, a substance in the body that causes allergic symptoms.
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Loratadine is also available in combination with pseudoephedrine (Sudafed, others). This monograph only includes information about the use of loratadine alone. If you are taking the loratadine and pseudoephedrine combination product, read the information on the package label or ask your doctor or pharmacist for more information.
Cimetidine Overview
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Cimetidine is used to treat ulcers; gastroesophageal reflux disease (GERD), a condition in which backward flow of acid from the stomach causes heartburn and injury of the food pipe (esophagus); and conditions where the stomach produces too much acid, such as Zollinger-Ellison syndrome. Over-the-counter cimetidine is used to prevent and treat symptoms of heartburn associated with acid indigestion and sour stomach. Cimetidine is in a class of medications called H2 blockers. It decreases the amount of acid made in the stomach.
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Definitions
Severity Categories
Contraindicated
These drugs, generally, should not be used together simultaneously due to the high risk of severe adverse effects. Combining these medications can lead to dangerous health outcomes and should be strictly avoided unless otherwise instructed by your provider.
Major
This interaction could result in very serious and potentially life-threatening consequences. If you are taking this drug combination, it is very important to be under close medical supervision to minimize severe side effects and ensure your safety. It may be necessary to change a medication or dosage to prevent harm.
Moderate
This interaction has the potential to worsen your medical condition or alter the effectiveness of your treatment. It's important that you are monitored closely and you potentially may need to make adjustments in your treatment plan or drug dosage to maintain optimal health.
Minor
While this interaction is unlikely to cause significant problems, it could intensify side effects or reduce the effectiveness of one or both medications. Monitoring for changes in symptoms and your condition is recommended, and adjustments may be made if needed to manage any increased or more pronounced side effects.
Onset
Rapid: Onset of drug interaction typically occurs within 24 hours of co-administration.
Delayed: Onset of drug interaction typically occurs more than 24 hours after co-administration.
Evidence
Level of documentation of the interaction.
Established: The interaction is documented and substantiated in peer-reviewed medical literature.
Theoretical: This interaction is not fully supported by current medical evidence or well-documented sources, but it is based on known drug mechanisms, drug effects, and other relevant information.
How To Manage The Interaction
Provides a detailed discussion on how patients and clinicians can approach the identified drug interaction as well as offers guidance on what to expect and strategies to potentially mitigate the effects of the interaction. This may include recommendations on adjusting medication dosages, altering the timing of drug administration, or closely monitoring for specific symptoms.
It's important to note that all medical situations are unique, and management approaches should be tailored to individual circumstances. Patients should always consult their healthcare provider for personalized advice and guidance on managing drug interactions effectively.
Mechanism Of Interaction
The theorized or clinically determined reason (i.e., mechanism) why the drug-drug interaction occurs.
Disclaimer: The information provided on this page is for informational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional regarding your specific circumstances and medical conditions.
Where Does Our Information Come From?
Information for our drug interactions is compiled from several drug compendia, including:
The prescribing information for each drug, as published on DailyMED, is also used.
Individual drug-drug interaction detail pages contain references specific to that interaction. You can click on the reference number within brackets '[]' to see what reference was utilized.
The information posted is fact-checked by HelloPharmacist clinicians and reviewed quarterly.